Lots to wade thru here....so I'll just make a few points.

It sounds like he has the drum Tee with an adjustable valve in the rear line. That's all you need...ever. BUT, its possible he has the valve plumbed in BACKWARDS, that'd give the symptoms he describes.

I'm not much on power boosters, but the comments on drum booster runout on disc swaps (pedal pressure skyrocketing) are well taken.

Reversing the caliper mountings from OEM prevents the flex line from crossing the steering axis (unless you move the hardline and frame bracket) and can be real dangerous (hose goes taut, abrades, etc.)

Gotta run...

Rick